The speed of data processing and data transmission in devices in which semiconductors are used, for example, computers, is rapidly increasing. A speedup in these devices absolutely requires a speedup in data processing and data transmission in semiconductor chips. Moreover, it is important to increase the speed of data transmission in semiconductor packages including semiconductor chips.
When the frequency of input and output signals of a semiconductor chip has exceeded 1 GHz, normal signal transmission cannot be performed due to an increase in the influence of interference between electrical signals transmitted through thin metal wires each of which electrically connects an electrode of a semiconductor chip to a lead part of a lead frame. Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 2003-68780) describes a technique for reducing the mutual inductance between signals transmitted through thin metal wires and suppressing occurrence of crosstalk by crossing the thin metal wires.
Moreover, Patent Literature 2 (Japanese Unexamined Patent Application Publication No. 2007-525842) describes a technique for reducing the self inductance of bond wires by crossing the bond wires at multiple points so as to suppress changes in the operation of a circuit due to changes in the electrical characteristics of signal paths caused by the self inductance of the bond wires and traces in a semiconductor package.
Recently, differential signaling has been used for rapid transmission of signals to and from a semiconductor chip. Differential signaling is signaling for binding two signal lines together into a pair (signal line pair) and detecting the potential difference between the signal lines. In differential signaling, a signal in one of the two signal lines is set as a complementary signal to a signal in the other signal line, and the difference between the signal lines is taken. Thus, noise superimposed on the two signal lines with the same polarity can be canceled.
On the other hand, in Peripheral Component Interconnect (PCI) Express, a bus standard for communications between processors and peripherals, a data transfer rate of 2.5 Gbps in one direction and a data transfer rate of 5.0 Gbps in two directions are supported. Input and output signals of a semiconductor chip need to have a frequency (signal frequency) ranging from 1.5 to 3 GHz to implement these data transfer rates. Moreover, in PCI Express Generation 2, a standard next to PCI express, a further increase in the signal frequency is required.
In the case of such high frequency signal transmission, even when differential signaling is used, signals transmitted through a signal line pair will suffer from the influence (crosstalk) of leakage of signals from an adjacent signal line pair. Then, a problem such that normal signal transmission cannot be performed due to the occurrence of jitter and the like will arise.
Thus, an amount of crosstalk of −30 dB or less is considered to be necessary in a signal frequency range of 1 to 3 GHz to avoid the influence of an adjacent signal line pair.
Methods for solving this problem include a method for providing wiring lines for shielding (shielding wires) between a signal line pair and an adjacent signal line pair. However, in this method, since shielding wires, together with wiring lines for signals, are provided on a board of a semiconductor package, the wiring pitch is increased, and thus, the density of wiring lines is decreased. That is, the density of wiring lines on a board of a semiconductor package cannot be increased. Thus, the method for providing shielding wires has a problem in that the method cannot adapt to an increase in the number of pins and a reduction in the pitch in input and output signal terminals of a semiconductor chip.